So will Apple have to go even bigger than the iPhone 5's 4-inch display?

"There is no strong motivation for Apple to move from its current position as sales are strong," Sunnebo said, "but in the future as we near smartphone saturation point in developed markets, and the only way to drive real growth will be to steal customers from Android, this will be a crucial decision Apple will have to make."

He added that Kantar Worldpanel's ComTech research data indicates that consumers are generally unwilling to switch to a device with a smaller screen.

"This could prove a decisive factor in current Android consumers' next purchase (particularly as the gulf between Apple and Android screen sizes widens)," he said.

Apple leads for now, though

Sunnebo told TechRadar that although Apple's new devices typically allow the company to overtake Android for around three periods at time, he expects Apple's current lead to last slightly longer, since "the iPhone 5 is a whole new device."

He added that while Android is more attractive to feature phone users looking to upgrade to their first smartphone, those users tend to switch to iOS for their next device, according to Kantar Worldpanel's research.

Width of bar indicates importance of switch

Given the research that claims consumers don't like switching to devices with smaller screens, though, even first-time Android users may grow less likely to switch to iOS, especially if Android devices continue get bigger while iPhones remain the same size.

Kantar Worldpanel's ComTech research comes from large proprietary panels of individuals representative of the 16 plus population in multiple countries.

In the US alone, the firm conducts 260,000 interviews with consumers per year. That figure jumps to 2.2 million interviews globally.